This invention relates to glass fiber production and, more particularly, to a method of controlling the simultaneous winding of glass strands into more than one package in a fiber forming process.
In the textile industry, linear filament bundles, such as yarn, strand and roving, are wound into packages by a winder; this practice is employed in winding linear filament bundles in synthetic filament forming operations, such as those producing glass filaments gathered into strands.
Modern winders are capable of simultaneously winding the strands into more than one package at a controlled linear collection speed. However, temperature variations in a cross section of the feeder supplying the molten glass streams from which the filaments are withdrawn can produce filaments having nonuniform diameters, even though the same linear strand collection speed is used for each package. Consequently, simultaneously wound packages are not always the same size during their formation. The prior art has attempted to solve this problem by employing a sensor to detect when the larger of at least two packages has reached a predetermined size during the formation of the packages. When the larger package has been sensed the guide member or builder arm is moved away from the packages. A winder utilizing this type of control is disclosed in Shape, U.S. Pat. No. 3,897,021, which is assigned to the assignee of the present invention. While the system of Shape gives highly satisfactory results and represents a marked improvement over the winding techniques previously known in the art, I have now discovered that even more accurate control of the package formation can be achieved by utilizing the control system of the present invention.
In order to obtain acceptable package build in a winding process, the guide means must maintain proper pressure on the forming package surface. This pressure is applied to the package surface through the strand guide-eye, cantilever spring, and cam, as disclosed in U.S. Pat. No. 3,897,021; such apparatus is commonly referred to as a builder. As the package diameter increases, the pressure on the package surface increases through the cantilever spring deflection until a "target" or "trip" magnet on the spring approaches a predetermined position, that is determined and sensed by a proximity switch. When this switch senses the target, it actuates the builder causing it to recede. Therefore, the pressure maintained on the package surface is a function of the builder back-off or receding rate and the cantilever spring constant.
Insufficient pressure will result in a package having flared ends, and excessive pressure will cause the package ends to bulge. An oscillation between insufficient pressure and excessive pressure will result in a package with ridged ends. To build an acceptable package, an optimum pressure range must be maintained on the package's surface. The back-off control system disclosed in Shape relies on an "OR" type logic system, i.e., the builder back-off rate is determined by the faster building package. Therefore, if there are temperature variations across the bushing, i.e., one half of the bushing is producing filaments of a larger diameter resulting in a heavier yardage than the other, the packages will have different diameter build rates. Consequently, the larger package causes the builder arm to back off before the smaller package has been built to a proper size; this results in the builder arm exerting insufficient pressure on the smaller package, thus causing the smaller package to have flared ends.
In addition to the problem of temperature variation across the bushing, the rate of package building decreases as the package builds, because of the increase in the diameter of the package. Prior art methods have merely moved the builder arm the same distance each time the larger package was sensed. Consequently, the prior art methods have not maintained a consistent pressure on the package throughout the building cycle.
Therefore, it is an object of this invention to provide a method of and apparatus for controlling the simultaneous winding of glass strands into more than one package in a filament forming operation such that the variance in the builder arm pressure on the simultaneously wound packages is reduced to a minimum, thereby providing packages of a uniform shape.